Power generating devices include geothermal power-generating devices other than thermal power-generating devices, hydroelectric power-generating devices and nuclear power-generating devices.
Geothermal power generation is carried out in the following way, as explained in non-patent document 1: Magma chambers with temperatures of around 1000° C. are located at a relatively shallow depth, several kilometers from the surface of the earth. Heat from the chambers heats rainwater that has permeated into the ground, which results in natural formation of a geothermal reservoir stratum in the earth. Into such a geothermal reservoir stratum is driven one or more pipes for production wells, the number of which is decided at need. A gas-liquid two-phase fluid-transferring tube is connected with the pipe, and gas-liquid two-phase fluid is transferred through the gas-liquid two-phase fluid-transferring tube to a steam separator. The fluid is divided into steam and hot water in the steam separator. The separated steam is sent through a steam pipe to a power-generating turbine. The steam introduced into the turbine rotates blades of the turbine, and the rotating power thus obtained rotates, in turn, the rotor of a generator. Electric power is thus obtained from the generator. On the other hand, hot water separated in the steam separator is sent through a hot water-returning tube to a reinjection well and returned deep in the ground.
Geothermal power plants are normally constructed in areas where geothermal reservoir strata are formed. Such areas are places often designated as national parks or called hot-spring resorts. Therefore it is difficult to employ staff members sufficient to operate a power plant and to construct installations and facilities necessary to operate a power plant.
A geothermal plant generates several tens kilowatts of electric power, which is small compared with several hundreds to a million kilowatts of electric power generated by a thermal power-generating plant. As a result, a geothermal power plant constructed at a remote and secluded place among the mountains is normally operated by a limited number of staff members for economic reasons.
It is difficult to control the characteristics of steam from one minute to the next in a geothermal power plant operated by a small number of staff members. Currently, control of the steam characteristics depends on, for example, a manual analysis that is carried out approximately once a month. More specifically, steam taken from a production well is cooled to condensate, and a water sample is taken out of the condensate. The water sample is sent to an analysis center, remote from the geothermal power plant, and the sample is manually analyzed at the center. It takes time for the staff members in the plant to have results of the manual analysis. Therefore when they find deterioration in the steam characteristics, the power-generating facilities may have already had trouble and operation of the geothermal power plant may have been fatally affected.
Problems with a power-generating turbine may include solid matter adhering to the blades of the turbine, or corrosion crack occurring in the surface of a blade caused by chloride ions, which may result in malrotation of the turbine blades. Another problem associated with operation of a geothermal power plant may be changes in the degree of vacuum in the condenser into which steam having worked in the turbine is sent, caused by unexpected changes in the amount of non-condensable gas in the steam. Generally, steam sent into a condenser is rapidly cooled to condensate, which creates a high degree of reduced pressure in the condenser. This high degree of reduced pressure increases revolutions of the turbine blades. In the field of geothermal power-generating devices, to bring the inside of the condenser into a high degree of reduced pressure is expressed as “to bring it into high vacuum”. When steam introduced into the condenser contains non-condensable gas, the condenser is not brought into a high vacuum state, which leads to a decrease in revolutions of the power-generating turbine. Therefore the inclusion of non-condensable gas in steam that will be sent to the condenser decreases the efficiency of power generation by the power-generating turbine.
The inventors of the present invention observed the surface of the blades when the power-generating turbine had problems such as irregularity in or incapability of revolution. As a result, they found that solid matter adhered to the surface. They also observed the surface of the blades to find whether there were cracks in the surface, and the observation revealed that it had stress corrosion cracking caused by chloride ions.
The steam separated from vapor-liquid two-phase fluid drawn from a production well for geothermal power generation contains various minerals. It is considered that when such a steam is sprayed onto the blades of the turbine, solid matter adheres to the surface of the blades, and that an increase in the amount of the solid matter causes the malfunctions mentioned hereinbefore. Also, a decrease in the degree of vacuum in the condenser due to changes in the amount of non-condensable gas in the steam that has worked in the turbine invites deterioration in the power generation performance of the power-generating turbine, which seriously affects the efficiency of power generation.
Therefore has been desired a steam characteristics automatic measuring device for geothermal power generation, capable of continuously and automatically carrying out analysis of the characteristics of steam which is introduced into a power-generating turbine and a condenser in a geothermal power-generating device which is operated and controlled by a few staff members; and informing engineers of the characteristics of steam at a location remote from the geothermal power-generating device, as well as a geothermal power-generating device equipped with the measuring device.
Non-patent document 1: “Thermal and Nuclear Power Generation”, by Thermal and Nuclear Power Engineering Society, the October, 2004 issue, page 7 and pages 10-14